A large portion of the U.S. meat supply may be contaminated with drug-resistant strains of the bacteria Staphylococcus aureus, a new study found.

While it's not known if such contamination is a threat to human health, since the bacteria would likely be destroyed by cooking, the findings are concerning, the researchers say. Staphylococcus aureus can cause disease in humans, including skin infections, or staph infections, pneumonia and sepsis. The bacteria also are responsible for methicillin-resistant Staphylococcus aureus , or MRSA, which is a problem in hospitals.

It's possible that improper handling of uncooked meat contaminated with the bacteria could pose a health risk, the researchers say.

The researchers examined samples of beef, chicken, pork and turkey from 26 grocery stores in five U.S. cities: Los Angeles, Chicago, Fort Lauderdale, Fla., Flagstaff, Ariz., and Washington, D.C.

Forty-seven percent of the samples were contaminated with Staphylococcus aureus, the study found. About 50 percent of the tainted samples contained bacteria that were resistant to at least three types of antibiotics, the researcher say.

The study is the first to assess the prevalence of drug-resistant Staphylococcus aureus in the U.S. food supply. The U.S. government checks for other types of bacteria, but not Staphylococcus aureus.

The researchers suspect agricultural animals are a major source of the contamination . Industrial farms often house animals in close quarters, and as a result, need to give them antibiotics to prevent infections. A constant stream of antibiotics into the animals' systems can potentially fuel the prevalence of drug-resistant strains of Staphylococcus aureus.

Drug-resistant forms of bacteria leave physicians with fewer options to treat their patients, said study researcher Dr. Lance Price, of the Translational Genomics Research Institute in Phoenix.

"The fact that drug-resistant S. aureus was so prevalent, and likely came from the food animals themselves, is troubling, and demands attention to how antibiotics are used in food-animal production today," Price said in a statement.

Future work will need to assess the risks of this contamination to the consumer, the researchers say.

The findings were published today (April 15) in the journal Clinical Infectious Diseases.

Pass it on: Close to 50 percent of meat samples tested from U.S. grocery stores are contaminated with the bacteria Staphylococcus aureus.

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